Which of the following best describes a VPLS?

Question Analysis

Question: Which of the following best describes a VPLS?

Provided Answer: C

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Correct Answer: C — Layer 2 multipoint-to-multipoint service

Explanation:

VPLS (Virtual Private LAN Service) is a Layer 2 VPN technology that emulates a LAN segment across a provider's IP/MPLS backbone network. Because a LAN inherently allows any device to communicate with any other device on the same broadcast domain, VPLS provides multipoint-to-multipoint (any-to-any) connectivity at Layer 2.

Key defining characteristics of VPLS:
- It operates at Layer 2 (Ethernet), forwarding based on MAC addresses.
- It performs MAC learning and floods broadcast/multicast/unknown-unicast traffic, exactly like a bridge/switch.
- It connects multiple customer sites together as if they were on the same Ethernet LAN — hence multipoint-to-multipoint.

This directly matches option C.

Why the Other Options Are Wrong:

- A. Layer 3 direct Internet access service — Incorrect. VPLS is a Layer 2 service, not a Layer 3 service, and it is a private LAN emulation, not Internet access.

- B. Layer 2 point-to-point service — Incorrect. A point-to-point Layer 2 service describes VLL (Virtual Leased Line) / VPWS (Virtual Private Wire Service / Epipe), not VPLS. VPLS is specifically multipoint, distinguishing it from these point-to-point services.

- D. Layer 3 IP multipoint-to-multipoint VPN service — Incorrect. This describes an IP VPN (RFC 4364 / BGP-MPLS IP VPN), which operates at Layer 3 using IP routing. VPLS operates at Layer 2.

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References:

1. RFC 4761 — Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling, IETF (Kompella & Rekhter), Section 1 ("Introduction"): defines VPLS as a service emulating a LAN, providing multipoint connectivity. https://doi.org/10.17487/RFC4761

2. RFC 4762 — Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling, IETF (Lasserre & Kompella), Section 1 and Section 3: describes VPLS as a Layer 2 service emulating an Ethernet bridge with MAC learning and any-to-any (multipoint) connectivity. https://doi.org/10.17487/RFC4762

3. RFC 4664 — Framework for Layer 2 Virtual Private Networks (L2VPNs), IETF (Andersson & Rosen), Sections 3.2 & 3.3: distinguishes VPWS (point-to-point) from VPLS (multipoint-to-multipoint) Layer 2 services. https://doi.org/10.17487/RFC4664

4. RFC 4364 — BGP/MPLS IP Virtual Private Networks (VPNs), IETF (Rosen & Rekhter), Section 1: defines the Layer 3 IP VPN model (contrast to option D, which is not VPLS). https://doi.org/10.17487/RFC4364

5. Nokia (Alcatel-Lucent) Service Routing Architecture — Services Overview documentation (7750 SR OS Services Guide), "VPLS Service Overview" section: defines VPLS as a multipoint Layer 2 VPN that provides connectivity between multiple sites as if on a single bridged Ethernet LAN, contrasted with Epipe (VLL) as a point-to-point Layer 2 service.

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Final Verified Answer: C — Layer 2 multipoint-to-multipoint service ✅

A. Layer-3 direct Internet access – VPLS is Layer-2 and does not provide routed Internet access.
B. Layer-2 point-to-point – that is VPWS/Epipe, not VPLS.
D. Layer-3 IP multipoint VPN – describes an IP-VPN (RFC 4364), not VPLS.

1. Nokia “SR OS Service Guide”, Release 22.5.R1, Section 8.1 “Virtual Private LAN Service (VPLS) – Overview”, p. 305.

2. RFC 4762 “VPLS Using LDP Signaling”, Sec. 1: “A VPLS presents an Ethernet LAN emulation, multipoint-to-multipoint service.”

3. MIT OCW 6.897 “Advanced Topics in Computer Networks”, Lecture 9 notes, p. 5: identifies VPLS as “L2 multipoint VPN”.